This invention relates to gas detectors and more particularly to improvements in solid state gas detectors.
Gas detecting apparatus exists which uses semiconductor material as a gas detector. Usually the apparatus operates on the basis of a direct semiconductor gas interaction. A measurement of the conductivity or resistivity of the semiconductor is taken as a indication of the presence and/or quantity of the particular gas for which the semiconductor is sensitive. Another technique is to detect a change in the rectifying or conducting properties of semiconductor diodes when exposed to gases. There are two basic problems with these prior art systems. One of these is that for the case of direct semiconductor/gas interaction, chemical interactions leading to the electrical response of the semiconductor are not usually reversible so that the signal output for a given gas pressure depends on the previous history of the semiconductor. That is, the gas/solid reaction proceeds deep in the semiconductor crystal for a lengthy exposure, and the changes deep in the crystal are slow and not reversible. Another problem, which has already been mentioned is that the reaction is slow.